1. Field of the Invention
The present invention relates to a thin-film transistor panel for use in an active matrix liquid crystal display element.
2. Description of the Related Art
A thin-film transistor panel (herein after referred to a TFT panel) for use in an active matrix liquid crystal display element comprises a plurality of gate lines and a plurality of data lines formed on a transparent substrate made of glass or the like, a plurality of thin-film transistors arranged at intersections of the lines, and pixel electrodes arranged in a matrix, respectively connected to the thin-film transistors. The thin-film transistors are of inverse stagger type.
FIG. 6 shows a portion of the above-described conventional TFT panel and FIG. 7 shows an electrical equivalent circuit thereof.
The TFT panel comprises a plurality of transparent pixel electrodes 2 arranged in row and column directions, a plurality of thin-film transistors 3 respectively connected to the pixel electrodes 2, and a plurality of gate lines G and data lines D connected to the thin-film transistors 3. Each gate line G is interposed between adjacent pixel electrode columns and each data line D is interposed between adjacent pixel electrode rows.
Each of the thin film transistors 3 comprises a gate electrode Ga connected to the gate line G formed on the substrate 1, a gate-insulating film 4 which covers the gate electrode, a semiconductor layer 5 formed on the gate-insulating film 4, and source and drain electrodes Sa and Da formed on the semiconductor layer 5. The gate-insulating film 4 of the thin-film transistor 3 is formed to cover the gate lines G substantially entirely over the substrate 1.
The pixel electrode 2 and the data line D are formed on the gate-insulating film (transparent film) 4. The source electrode Sa of the thin-film transistor 3 is connected to the pixel electrode 2 and the drain electrode Da to the data line D.
The TFT panel is adhered by a frame-like sealing material to an opposite panel (not shown), which is obtained by forming an opposite electrode (transparent electrode) on a transparent substrate and orientating the electrode. Liquid crystal is injected between the two panels, thereby producing an active matrix liquid crystal display element.
In the active matrix liquid crystal display element, each pixel electrode 2 in the TFT panel has a storage capacitor Ca in order to suppress the variation of potential maintained by the pixel electrode 2 in a non-selection period.
In FIGS. 6 and 7, a reference symbol C denotes a capacitor line which constitutes the storage capacitor Ca. The capacitor line C is formed on the substrate 1 (under the gate-insulating film 4), so as to face one side of the pixel electrode of each line and extend in parallel with the gate line G.
The storage capacitor Ca is formed of the capacitor line C, the pixel electrode 2 and the gate-insulating film 4 interposed therebetween. It stores charges applied to the pixel electrode 2 during a selection period (when the thin-film transistor 3 is in an ON state). By virtue of the storage capacitor Ca, the potential in the pixel electrode 2 in the non-selection period is maintained. The capacitor line C is connected to a reference potential (ground potential).
The above-described TFT panel is, however, disadvantageous in that a number of lines must be used. More specifically, capacitor lines C of a number which coincides with the number of the pixel electrode columns are required, since one capacitor line C is provided in one pixel electrode column.